A residual film or a concave scratch may be formed on a back surface of a substrate to be processed which has been performed various processes such as forming, etching or the like in an LSI production. When the back surface of the substrate is fixed on a stage in lithography process, the substrate is distorted due to the residual film or the concave scratch. As a result, a flat standard surface cannot be formed on the surface of the substrate to deteriorate the lithography process. Therefore, solving the back surface of the substrate by a chemical solution has been performed.
On the other hand, as a silicon oxide film, a silicon nitride film or the like is deposited on the back surface of the substrate, it is difficult to collectively solve these films with high speed. Further, even if these films are collectively solved, a concave scratch is leaved.
Polishing the back surface of the substrate can be considered for a method to collectively remove the residual film or the concave scratch. In the polishing, the back surface of the substrate, which is polished, is applied with polishing load 100-500 hPa, for example. Accordingly, a substrate retaining mechanism is necessary to support the polishing load. It is desirable that a retaining plate is disposed at a surface side opposite to the surface to be polished.
When the back surface of the substrate is polished in a LSI production, the front surface with a LSI structure of the substrate is retained. Consequently, a fine LSI structure can be damaged or contaminated.
As another method for retaining a substrate, a method of holding only a side surface has been known. However, the substrate is distorted with increasing the polishing load. Especially, distortion amount in a center of the large scale substrate becomes large, therefore, polishing cannot be effectively performed and is capable of relating to crystalline defects or crack of the substrate. Furthermore, as the substrate is polished with high speed, suitable polishing load is necessary. Accordingly, the retaining method fixing the side surface is not fit to the polishing processing.